Universal Heatplate from old 3D Printer

First of all: I'm not an expert in PCB design or electronics so I'm open to feedback what I can do better :)

I needed a hotplate for a phone repair, but just had an old 3D Printer Hotbed laying around.
So I thought, I give it a new purpose.

The Hotplate can reach temperatures up to 90°C.

The PCB Design is based on standard perf board, so it's easier to do at home.

The Hotbed used was in my case a 12V one from a FreeSculpt 3D ex1.

Parts List:
Hardware:
1x 12V Hotbed from 3D Printer
1x "3D- Freunde" V2 Mosfet (https://amzn.to/3bNbzUJ) (Others will work too)
1x 12V 5A Powersupply (https://amzn.to/2JrzVXV)
1x Another Arduino board for programming the Pro Mini
Xx Some Cables and Plugs for connections to Hotplate, etc.

Components for PCB: (In the Thing files you will find a more detailed parts list)
1x 90x58mm perf board
1x Arduino Pro Mini (3.3V 8Mhz)
1x 7-Segment Display
1x DC-Input Jack
1x PNP Transistor S8050
1x 3x2 Male Header
1x 1x2 Male Header
8x 100 O